Previously a receiver of radio waves such as AM/FM has been arranged on a vehicle.
Recently, forming a unit in advance by mounting an antenna as a plate shaped structure within a casing and during a manufacturing process of a vehicle fixing the vehicle antenna unit to the roof of a vehicle and connecting the antenna mounted in within the vehicle antenna unit to a receiver installed in the vehicle has become a common process based on the knowledge that it is possible to form an antenna with respect to a constant radio wave as a plate shaped structure (metal plate or a circuit board formed with an antenna pattern) as an antenna for receiving these radio waves.
However, since the distance of a non-folding antenna unit from a roof of a vehicle is regulated to approximately 7 cm, an antenna having a low height from the roof is desired as a circuit board and plate shaped antenna mounted in an antenna unit due to this regulation.
Moreover, since a vehicle roof or a base of an antenna unit in contact with the roof is a manufactured from metal in order to earth the vehicle, ineffective capacity is produced between the roof or base and the antenna which causes a drop in antenna gain. In order to avoid such as drop in gain, an antenna pattern or antenna coil on the surface of a circuit board must be arranged at a position of a height sufficiently separate from the roof. However, in an antenna unit mounted only with a circuit board, it is difficult to form an antenna pattern with a length corresponding to an AM wavelength on the circuit board. As a result, an antenna unit is proposed in which a plate shaped antenna is arranged alone or combined with a circuit board while the effective capacity of the entire antenna is maintained.
For example, in Japanese Patent Application Laid-Open Publication No. 2012-15836 (referred as “patent document 1”), an antenna unit (a roof compatible mount antenna) is disclosed including a structure in which a compound antenna formed by fixing a short axis coil element 101 to the rear side of a radio antenna (plate antenna element) 100 formed by bending a metal plate into a gable roof mold is fixed to an interior surface of a synthetic resin cover (antenna cover) 102 by double sided adhesive tape or adhesive bond as is shown in the FIG. 10 attached to the present specification.
In addition, an antenna unit including a structure in which an antenna substrate formed by mounting an antenna coil as well as forming an antenna pattern on a surface of a circuit board is fixed perpendicularly on a metal base plate (antenna base) and completely covered by a synthetic resin cover (antenna cover) is disclosed in FIG. 1 to FIG. 17 of PCT Patent Application Publication No. 2008/062746 (referred as “patent document 2”), an antenna unit (antenna device) including structure in which a gable roof plate shaped antenna (top) is fixed on an upper edge of an antenna substrate formed by mounting an antenna coil as well as forming an antenna pattern on a surface of a circuit board is disclosed in FIG. 18 of the same document, and an antenna unit (antenna device) including a structure in which an antenna comprised from a metal rod having a triangular cross-sectional shape is supported on a base plate (antenna base) and is conductive with a coil antenna is disclosed in FIG. 66 of the same document.